Probably many factors.

-As OP said, no longer making the Bonneville America. Sure, there are still some around but a lot of people who were so active here have moved on to other rides. If a new BA owner finds this forum, there isn't much current discussion to keep them interested.

-Rallies are fewer and farther between. That's how I found this forum before we bought an America LT. I saw a sign pointing to a meeting place for the Noreast rally and followed it to the campground of a group of BA.com members that I rode with few times. The Noreast rally no longer exists. I wanted to ride to the Arkansas rally this year, but the COVID-19 restrictions are keeping me away.

-I am an American and am also turned off by the political discussions on a motorcycle forum. Just don't belong. Don't worry. I won't be flinging bullets. That's the other side of the political divide here in the US.